1. Field of the Invention
The present invention relates to a fuel injector.
2. Description of the Related Art
A fuel injector, which includes an electromagnetic actuation element having a solenoid coil, an internal pole and an external magnetic circuit component as well as a movable valve-closure element, which cooperates with a valve seat assigned to a valve-seat body, is already known from published German patent application document DE 38 25 134 A1. The fuel injector is surrounded by a plastic extrusion coat, the plastic extrusion coat extending primarily in the axial direction so as to surround the connecting piece that acts as the inner pole as well as the solenoid coil. At least in the region surrounding the solenoid coil, ferromagnetic filler materials conducting magnetic lines of force are embedded in the plastic coating. In this respect, the filler materials surround the solenoid coil in the circumferential direction. The filler materials are fine-grained broken-up pieces of metal having soft-magnetic properties. The small metal particles embedded magnetically in the plastic have a more or less globular shape and are individually magnetically isolated and thus have no metallic contact among one another such that no effective magnetic field is formed. The positive aspect of a very high electrical resistance arising in this connection, however, is countered by an extremely high magnetic resistance, which is reflected in a substantial loss of force and thus determines the overall negative functional properties.
Furthermore, a fuel injector is known from published German patent application document DE 103 32 348 A1, which has a relatively compact design. In this valve, the magnetic circuit is formed by a solenoid coil, a fixed inner pole, a movable armature and an outer magnetic circuit component in the form of a magnetic cup. To achieve a slim and compact construction of the valve, multiple thin-walled valve sleeves are used, which act both as connection piece and as a valve-seat support and guide section for the armature. The thin-walled non-magnetic sleeve extending inside the magnetic circuit forms an air gap, via which the magnetic line of force pass over from the outer magnetic circuit component to the armature and the inner pole. A fuel injector of a comparable type of construction is shown again in FIG. 1 and is subsequently explained in more detail for a better understanding of the present invention.
Furthermore, a fuel injector is already known from published Japanese patent application document JP 2002-48031 A, which is likewise characterized by a thin-walled sleeve approach, the deep-drawn valve sleeve extending over the entire length of the valve and having a magnetic isolation point in the magnetic circuit region, in which the otherwise martensitic structure is interrupted. This non-magnetic intermediate section is situated at the level of the region of the working air gap between the armature and the inner pole and in relation to the solenoid coil so as to create a magnetic circuit that is as effective as possible. Such a magnetic isolation is also used in order to increase the DFR (dynamic flow range) compared to the known valves having conventional electromagnetic circuits. Such constructions, however, are bound up with substantial additional costs in their manufacture. Moreover, the introduction of such a magnetic isolation by a non-magnetic sleeve section results in a different geometric layout compared to valves without magnetic isolation.